1. Field of the Invention
The present invention relates to an electroconductive elastic member and an electrophotographic apparatus using the same. More particularly, the present invention pertains to an electroconductive elastic member which is lessened in not only positional variance of electric resistance but also dependence of electric resistance upon applied voltage as well as in variation range of electric resistance at the time of continuous passage of electric current and variation in electric resistance due to environmental change, and which is well suited as an elastic roller with an intermediate electric-resistance for use in an electrophotographic process; to an electroconductive elastic member which is imparted with an antistatic function such as a packaging member and a shock-absorbing member, or a developing member and an image transfer member that are employed in an electrophotographic mechanism; and to an electrophotographic apparatus using any of the above-mentioned electroconductive elastic members.
2. Description of the Related Arts
In the electrophotographic process including a copying machine, an electrostatic recording apparatus or the like, there has heretofore been generally adopted a copying method which comprises the steps of at first, uniformly electrically charging the surface of a photosensitive body in which is used a photoelectroconductive substance, for example, ZnO, CdS, Se, OPC(organic photoconductor), .alpha.-Si and the like; thereafter projecting an image thereonto from an optical system to lower the potential of the part which has been stricken by the light from the optical system, thereby forming a latent image; and subsequently carrying out the adhesion of a toner (development) and transfer of the toner image to a transfer material (recording medium) such as paper.
In the above-mentioned electrophotographic process, intense attention has been paid to an electroconductive elastic member, which is utilized in the form of an elastic roller having an intermediate electric-resistance and the like members. In this elastic roller having an intermediate electric-resistance and the like members, use is usually made of a high molecular elastomer or a high molecular foam such as rubber and polyurethane as a matrix.
The elastic roller having an intermediate electric-resistance which is used for the above-mentioned purpose of application is required not only to possess a prescribed electric-resistance but also to be lessened in positional variance of electric resistance, in dependence of electric resistance upon applied voltage, in variation range of electric resistance at the time of continuous passage of electric current and besides in variation of electric resistance due to change in environmental conditions such as temperature and humidity. In order to meet the aforesaid requirements, therefore, various materials have heretofore been investigated, however none of said materials has sufficiently met the requirements.
In the case of intermixing, for example, carbon black as an electroconductive material in an electroconductive elastic member, the problem still remains unsolved in that it is difficult to keep the electric resistance constant in the intermediate electric-resistance region in the range of 1M.OMEGA. to 100G.OMEGA. which range is needed for an electrophotographic process. Likewise, a high molecular elastomer, a high molecular foam and the like that are regulated to a prescribed electric resistance by intermixing therein a powder or a whisker of a metal or a metal oxide, or a filler such as carbon black suffer the problems of great positional variance of electric resistance and remarkable dependence of electric resistance upon applied voltage. In order to solve the above-mentioned problems under such circumstances, an attempt is made to produce an electroconductive elastic roller having a definite electric resistance in the intermediate electric-resistance region by intermixing therein an tonically electroconductive substance such as a specific salt exemplified by lithium perchlorate, sodium perchlorate and calcium perchlorate. Nevertheless, such rollers bring about unfavorable situations including much difference in electric resistance between the circumstances of a high temperature and a high humidity such as 32.5.degree. C./85% R.H. and those of a low temperature and a low humidity such as 15.degree. C./10% R.H.; gradual increase in its electric resistance with long-term continuous running under the conditions of electric current passage; and besides the occurrence of poor image in the case of the roller being used for electrophotography. Although the mechanism of the increase in the electric resistance is not necessarily clarified, it is thought that the salt such as lithium perchlorate, sodium perchlorate and calcium perchlorate which is added to the roller for the manifestation of electroconductivity is subjected to dissociation and polarization, whereby electric current is made difficult to pass, and at the same time, the electric resistance is increased thereby.
It has previously been found by the present inventors that a polyurethane material is obtained which has a characteristic volume resistivity in the range of 10M.OMEGA..multidot.cm to 1000G.OMEGA..multidot.cm and which is stabilized in electric resistance even during a long time of electric current passage by using, as a matrix, a polyurethane foam or a polyurethane elastomer which is produced from any of tolylene diisocyanate, diphenylmethane diisocyanate and crude diphenyl-methane diisocyanate each as a starting raw material and at the same time, by adding thereto a quaternary ammonium salt as an tonically electroconductive substance refer to Japanese Patent Application Laid-Open No. 113050/1995 (Hei-7)!. However, the above-mentioned material is not necessarily satisfactory because of much difference in the electric resistance between the circumstances of a low temperature and a low humidity such as 15.degree. C./10% R.H. and those of a high temperature and a high humidity such as 32.5.degree. C./85% R.H.
On the other hand, eager and increasing demands have recently been imposed on an electroconductive elastic member to be well suited for use as a packaging member and a shock-absorbing member in which antistatic function is required for the purpose of protecting electronic part items.